This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 101 15 172.1, filed on Jun. 8, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates generally to air jet weaving looms and particularly to the monitoring of the weft insertion in an air jet weaving loom, particularly downstream of the exit of the weft insertion channel.
German Patent Publication DE 44 43 371 C1 corresponding to U.S. Pat. No. 5,606,998 (Wahhoud et al.) discloses a weft thread stretching mechanism and a weft thread detection or monitoring device for jet weaving looms. The main purpose of the disclosure of U.S. Pat. No. 5,606,998 is to avoid identifying a temporary excess length of the leading end section of a weft thread that occurs due to stretching of the weft thread, as a weft thread break. More specifically, the temporary excessive weft thread length at the leading end section of the weft thread shall not lead to stopping the weaving loom. The excess length is temporarily caused by exposing the leading end of the weft to a stretching operation by a stretching jet that is effective to blow the leading end of the weft thread in a direction perpendicularly to the feed advance direction defined by the longitudinal axis of the weft insertion channel. The stretching jet blows the leading end of the weft through a stretching channel extending in a plane laterally displaced from the plane defined by the feed advance direction. For this purpose, the monitors or so-called weft stop motion devices are arranged at the end of the stretching channel or path. Additionally, the axial length of the stretching channel is adjustable. In order to accommodate this adjustable length of the stretching channel, the position of the weft stop motion devices at the end of the stretching channel is also adjustable in the axial direction of the main weft insertion channel of the loom. Such a structure avoids identifying a temporary excess length that occurs due to the stretching of the weft thread as a weft break. As a result, the loom operation is not erroneously shut down. Only when the leading end of the weft does not pass all the way through the stretching channel will the loom stopping signal be generated.
German Patent Publication DE 195 45 839 C1, corresponding to U.S. Pat. No. 5,735,316 (Hehle) relates to a method and apparatus in an air jet weaving loom for avoiding the formation of a so-called catch selvage. Instead, a leading end of the inserted weft thread is stretched by a special deflecting weft stretching jet nozzle and the deflected end is cut off and withdrawn by suction. A first weft stop motion device is positioned at the exit of the weft insertion channel upstream of the stretching nozzle. A second weft stop motion device is positioned downstream of the stretching channel.
German Patent Publication DE 198 02 254 C1 corresponding to U.S. Pat. No. 6,082,413 (Scorl et al.) relates to a weft thread stretching and detecting mechanism for air jet weaving looms in which again the leading end of the weft thread is deflected by a stretching nozzle into a separate stretching channel that extends in a plane different from the plane defined by the longitudinal axis of the weft thread insertion channel. A first weft stop motion device is arranged upstream of the catch selvage and upstream of the deflecting stretching nozzle. A single second weft stop motion device is arranged at the exit end of the stretching channel and at the end of the extension of the weft insertion channel. A beam transmitter and a beam sensor are so arranged relative to each other at the exit ends of the stretching channel and of the insertion channel so that the beam must cross the exits of both channels. This position of the weft stop motion device can monitor both the insertion channel and the stretching channel in order to ascertain whether an excessively long weft thread or a broken weft thread is involved.
European Patent Publications EP 0,493,847 A1 (Bamelis) and EP 0,645,485 A1 (Granelli et al.) disclose different types of stretching channels. In both instances the weft stop motion device is arranged upstream of the stretching channel at the exit of the insertion channel.
In all known devices with a stretching channel that is either aligned with the insertion channel or is positioned in a different plane from the plane of the insertion channel, it is not excluded that a leading end section of the weft thread is deformed, for example by the formation of a loop or kink. The positioning of the weft stop motion devices according to the prior art does not enable these devices to ascertain whether a leading end section of a weft thread has been deformed. If a weft thread with a loop or a kink in its leading end section is beat-up into the fabric, the resulting fabric does not meet the required quality.
In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination:
avoid weaving a weft thread deformation, particularly a loop or a kink at the leading end section of a weft thread into the fabric;
to position either an additional weft stop motion device or the so-called first weft stop motion device in a location where the weft thread deformation, particularly at the leading end of the weft thread can be positively discovered for producing a control signal that will cause a corrective action in the loom operation; and
to generate a loom stop signal in response to the absence of the leading end of the weft thread in the stretching channel and to evaluate the presence of the leading end of the weft threads in the stretching channel as a weft thread that has not been deformed.
The above objects have been achieved according to the invention in a method for detecting a deformation such as a loop or a kink in a leading end section of a weft thread exiting from a weft insertion channel in an air jet weaving loom by performing the following steps:
(a) positioning an additional weft stop motion device (10) in an entrance area of a weft stretching path,
(b) exposing said leading end section of said weft thread to a stretching force in said weft stretching path downstream of said weft insertion channel,
(c) monitoring with said additional weft stop motion device (10) a presence or absence of a leading end (7B) of said leading end section (7A) of said weft thread (7) in said entrance area of said weft stretching path downstream of said waft insertion channel, and
(d) generating a loom control signal in response to said presence or absence of said leading end (7B) in said entrance area of said weft stretching path.
Positioning the weft stop motion device in an entrance area of the weft stretching path allows monitoring the arrival and any deformation of the leading end section of a weft thread.
The method according to the invention is performed by an apparatus that comprises a weft stretching channel positioned downstream of the weft insertion channel. The weft stretching channel has an entrance area where a jet nozzle is positioned for seizing the leading end section of the weft thread and driving the weft thread into the entrance area of the weft stretching channel and then through the weft stretching channel. According to the invention, a weft stop motion device is positioned in the weft stretching channel or rather in a position for monitoring the passage of the leading weft thread end through the stretching channel to thereby ascertain the presence or absence of the leading end section of the weft thread in the weft stretching channel.
The weft stretching channel may be positioned in axial alignment with the longitudinal axis of the weft insertion channel or it may be positioned in a plane other than a plane defined by the longitudinal axis of the weft insertion channel. In both instances the weft stop motion device will be positioned to monitor the presence or absence of the leading end section of the weft thread in the stretching channel.
It is customary to refer to the weft stop motion device that is positioned at the exit end of the weft insertion channel as the first weft stop motion, while the weft stop motion device at the exit end of the stretching channel is referred to as the second weft stop motion. It has been found that the positioning of a weft stop motion device at the exit end of the weft insertion channel merely determines the arrival of a leading weft thread end at the exit. In such a position at the exit of the weft insertion channel the weft stop motion device cannot determine whether or not there is a deformation in the end section of the leading weft thread end that has come out of the exit of the weft insertion channel. In order to detect a weft end deformation it is critical to position at least one weft stop motion device in a location for monitoring the stretching of the weft leading end section in the stretching channel or path to thereby determine the presence or absence of the leading end section of the weft thread in the stretching channel. Thus, in an apparatus according to the invention either an additional weft stop motion device is positioned relative to the stretching path or channel or the so-called first weft stop motion device is placed further downstream for monitoring the weft thread end in the weft stretching path or channel. In that case, the so-called xe2x80x9cfirstxe2x80x9d weft stop motion directly at the exit of the weft insertion channel is not used at all. Thus, if the leading end section does not appear in the stretching channel or path or is too short because of a loop upstream of the stretching channel, a loom stop signal is generated.
It has been further found, that the formation of a deformation such as a loop or kink in the leading end section of the weft thread happens particularly when the weft thread is deflected by a stretching jet out of the plane of the weft insertion channel into another plane in which the stretching channel is located. The blowing of the leading weft end into the stretching path or channel results in a temporary lengthening which is detected by positioning the weft stop motion as taught by the invention relative to the weft stretching path or channel and not necessarily at the exit end of the weft insertion channel. Thus, a single weft stop motion device placed for monitoring the stretching path or channel can detect the predetermined length that results from the stretching and a possible loop signifying that the leading weft thread end section does not have the proper xe2x80x9clengthxe2x80x9d due to the loop formation. In that case, the leading end does not reach the weft stop motion device in the stretching channel and the further loom operation is stopped. No stopping of the loom occurs when the leading end of the weft thread reaches the conventional xe2x80x9cfirstxe2x80x9d weft stop motion device if no break in the weft thread has occurred.
By placing or locating the weft stop motion device for monitoring the stretching channel, the so placed weft stop motion performs the function of the so-called first weft stop motion device and of an additional weft stop motion device that detects not only the arrival of the leading end, but also whether or not a loop has been formed in the leading end section of the weft.